In power looms, heddle shafts are provided that are formed by a rectangular frame with heddles located in it. The heddle shaft has one or more heddle shaft rods, which are located transversely to the direction of motion of the heddle shaft and carry the heddle support rails for the heddles. The heddle shaft rods must be as lightweight and rigid as possible. To that end, it is known to make them from a lightweight hollow metal profile section. This is taught for instance by German Patent DE-PS 23 27 044.
There has long been a need to reduce the noise created by a power loom. The noise originates at least in part in the heddles, which are seated with some play on the heddle support rails. The reciprocating motion of the heddle shaft causes constant impacting or striking of the end eyelets of the heddles against corresponding stop faces of the heddle support rail. The noise thus engendered is considerable.
In response to this problem, the aforementioned German Patent DE-PS 23 27 044 proposes that the side walls, of the hollow metal profile section from which the heddle shaft is formed, be bulged inward somewhat, so that seen from outside, the side walls have a concave curvature. An inlay of acoustic damping material is then press-fitted into the hollow chamber enclosed by the side walls and presses the side walls outward, so that in the working position they extend parallel to one another. At least for relatively long heddle shaft rods, this provision is relatively difficult to execute. For that purpose the rails of acoustic damping material must be relatively rigid in the longitudinal direction, which in turn compromises their acoustic damping properties. This is all the more true when the acoustic damping element must be subject to a considerable clamping force, if it is to be capable of stressing side walls of the hollow metal profile section away from one another and thereby deforming them. It is thus hardly possible to produce long heddle shafts. It can furthermore prove difficult to adapt the lateral pressure precisely such that the previously concavely inward-curved side wall is actually straight in use, with the damping element inserted. If straightness is not attained, however, the bending strength of the hollow metal profile section is impaired, which can in turn cause difficulties.
It is also known from Japanese Patent Disclosure JP 61-159380 to fill a hollow chamber in a heddle shaft rod with a laminate, comprising a foam and rubberlike layers, for damping purposes; this laminate expands under the effect of heat. Equipping the hollow chamber of the heddle shaft rod with it and ensuing heating process are time-consuming and expensive. In addition, the heating process has the risk that the shape and structure of the heddle shaft rod will change.
All the known methods or constructions, if they involve introducing damping materials into the heddle shaft rod, have one or another disadvantage in terms of technology or manipulation.
With this as the point of departure, it is the object of the invention to create a heddle shaft rod which has an acoustic damping effect and is simple to produce and is furthermore unimpaired in its mechanical properties. It is also the object of the invention to furnish a method for producing such a heddle shaft rod and the utensils required for this.